The environmental impact of food, writes Gareth Edwards-Jones in this week's Green Room, is more than about how many miles it has travelled to get to your plate.
We are all used to buying goods that originate from abroad, be they toys from China, cars from Germany or clothes from India.
We don't hear too much about the environmental impacts of such imports, but we do hear a lot about food which is produced overseas.
Indeed, the terms "food miles" was coined in order to convey to the general public that an awful lot of food travels an awful long way before it finally reaches our mouths.
But food doesn't have to travel from an exotic location in order for it to clock up food miles. UK-produced food can also travel substantial distances between farm, processors, storage depot and the supermarket.
A lot of people object to this accumulation of food miles, and we seem to have increasing calls for "local food" and "slow food". While those making these calls may seem to have common sense on their side, the science which could be used to underpin their arguments is at best confusing, and at worst absent.
Diversity of reason
To start with, the advocates of local food don't speak with one voice and there seem to be several different reasons for calling for local food.
For example, social scientists are generally very much in favour of communities increasing the amount of interaction they have with each other, be it buying and selling or simply doing each other favours.
These sorts of interactions are felt to be important in forming and maintaining "sustainable communities". Local food initiatives help form sustainable communities as they encourage local processors and consumers to buy from local farmers, thereby making more social links while simultaneously keeping the money in the local community.
Some other groups, typically those representing farmers, seem to support local food initiatives as they tend to increase demand for their own produce - a kind of ethical "trade barrier".
However, perhaps most people support local food as they relate food miles with environmental damage.
Typically, attention concentrates on the greenhouse gases that are emitted by the vehicles which transport the food, be they trucks or aeroplanes.
So for many environmentally aware consumers, it is the desire to reduce greenhouse gas emissions which drives them to buy local food.
Unfortunately though, simply getting consumers to target food miles when making their purchasing decisions may not necessarily bring about a reduction in greenhouse gas emissions, as these are emitted from many more places within food systems than just trucks, planes and automobiles.
The energy in cooking food needs to be considered as well
For example, the production of fertiliser, pesticides, machinery and packaging all use energy - the generation of which will undoubtedly have contributed some greenhouse gases to the atmosphere.
In addition, storing and cooking food also consumes energy.
Indeed, our research suggests that when considering UK grown potatoes, 48% of all energy used during the potato's life cycle is expended in the kitchen (the life cycle encompasses the sowing, growing, harvesting, packaging, storage, transport and consumption of potatoes).
Boiling potatoes is horrendously energy intensive, and this simple act dwarfs the energy consumed during their production and transport.
But less obvious to the average consumer is the fact that soil itself produces greenhouse gases, and different types of soils produce different amounts of gas.
These gases, which include carbon dioxide, methane and nitrous oxide, are emitted by the millions of bacteria which live in the soil.
The gas emissions occur as the bacteria break down carbon-based molecules in the soil, most of which exist as organic matter (or humus).
As yet, we don't know much about how these emissions vary between different types of soils. Nor do we know if the way the crop is managed can alter the levels of gas emitted.
However, the research done to date does show that there can be big differences between different land uses. For example, emissions of carbon dioxide from grasslands are usually quite low, while those from paddy fields are higher.
We also know that there are variations in gas emissions from location to location - across countries and across Europe. But our knowledge is sketchy, and we know almost nothing about these gas emissions in tropical systems.
Such knowledge gaps are not unusual as our understanding of the science of food production and consumption is still in its infancy, and there is much we do not know.
But we do know enough to seriously question the scientific validity of simply using food miles as a proxy of environmental damage.
As a professional scientist, I need to recognise these "knowledge gaps" and then undertake some research that will hopefully fill them. As a consumer though, you need to eat, so what should you do?
At the moment, science can't help - as we simply don't know enough. My personal advice would be to do what ever best satisfies your conscience, but don't kid yourself that by so doing you are saving the world.
Confirmation of such cause and effect will require a lot more science be done.
Gareth Edwards-Jones is Professor of Agriculture and Land Use at the School of Agricultural and Forest Sciences, University of Wales, Bangor.
The Green Room is a weekly series of opinion articles on environmental issues on the BBC News website
Do you agree with Gareth Edwards-Jones?
Is there a 'knowledge gap' in our efforts? What else could be done to limit environmental harm done by farming, transporting, and eating our food?